Make examples/benchmark.cpp work with POCL
Make examples/benchmark.cpp work with POCL

POCL for some reason fails to compile a kernel where an int is assigned
to a double.

Poulpy21/vexcl,ddemidov/vexcl,kapadia/vexcl,Poulpy21/vexcl,ddemidov/vexcl,kapadia/vexcl,Poulpy21/vexcl